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Rosacea is a common skin condition, afflicting 16 million Americans with red, inflamed skin, usually in the middle of the face. At last, scientists think they know the cause, but it isn't pretty—the feces of tiny, spider-like mites that live in your pores, reports New Scientist. The mites are called Demodex, and scientists have known about them a long time. We all have them living in our pores, usually 20 to 30 per square inch of facial skin. They love to hang out around your eyebrows and eyelashes and eat your facial oil.

Gross, yes, but even grosser for people with rosacea: They can have up to 10 times the number of mites in their skin. Because Demodex mites don't have anuses, they don't poop, and their feces just builds up in their bodies until they die, usually inside our pores. For people with rosacea, when all those critters die, it releases a lot of fecal bacteria all at once, causing an immune reaction and inflammation. You can read an abstract of the original article at the Journal of Medical Microbiology.